1. Field of the Invention
The invention concerns a drive system, particularly for motor vehicles, specifically with the features taken from the preamble of claim 1.
2. Description of the Related Art
Drive systems, particularly mechanical drive systems with an integrated electrical machine functioning as a starter generator, are known in a plurality of designs. Reference is made by way of example to a compilation of Dr.-Eng. Wolfgang Reick, LuK & Co, Bühl, “Startergenerator im Antriebsstrang” [Starter Generators in the Drive Train”], published at http://www.luk.de/Bibliothek/Vortraege.html. A starter generator of this kind is understood here to refer to an electrical machine, the rotor of which is mounted directly on the crankshaft or else is arranged parallel to the latter and which can work both as a generator and as a motor. The electrical machine is employed for starting the internal combustion engine and, further, as a generator for energy recuperation from the drive system. In particular, the recuperation of energy in, for example, the coasting or decelerating mode is gaining ever increasing importance owing to the constant increase in the number of electrically driven components. In order to provide these functions, a certain dimensioning of the electrical machine is necessary and thus the system cannot be offered at an especially favorable price; therefore, additional functions are being increasingly assigned to this unit. Such additional functions are: start/stop function for soft start, direct start, impulse start, booster, energy recuperation in coasting, active synchronization, and damping. The electrical machine can be disposed here coaxially or eccentrically for the coupling between the internal combustion engine and the drive train, usually a transmission. Depending on the arrangement, the electrical machine is arranged through one or two clutches so that it can be disengaged from the drive train. A design of a starter generator for automatic transmissions with converter may be found on page 53 of the above article. In it, the starter generator is adjoined to the hydrodynamic speed/torque converter. In the structural space designed for the current lockup clutch, only one further second clutch is integrated, which can disengage the motor from the pump case. The first clutch serves here to make a connection between the crankshaft and the rotor and the second clutch represents the usual lockup clutch. If the first clutch is opened, the internal combustion engine can be stopped and the electrical machine will continue to operate. Accordingly, this allows all states that are possible with a two-clutch solution to be provided, that is, particularly the function as a booster and as a starter and the recuperation of energy. An important drawback of the use of a converter in the automatic transmission consists of the fact that, also particularly at low temperatures, in spite of the possibility of the direct start or of an impulse start via the electrical machine, the power transmission via the hydrodynamic converter is thereby very unsatisfactory, especially in low gear. The advantages that ensue through the use of the starter generator are in turn eliminated by the poor cold start behavior in this state, which, particularly for use in automatic transmissions or automated shift transmissions, can be problematic at corresponding latitudes with at times very low temperatures. Further, the complete unit consisting of electrical machine and starting component has a very wide construction in the axial and radial directions. The necessary structural space is defined here essentially by the structural space required for installing the hydrodynamic speed/torque converter and thus the still remaining possibilities available for integration of the electrical machine. A further important drawback consists in the nonexistence of a possibility for adjusting the power input and for control of the power input of the hydrodynamic speed/torque converter. Accordingly, in all operating states, the maximum power possible is immediately taken up by the latter and this can lead, under certain circumstances, to an undesired driving response during starting operation and possibly also to a sudden stalling of the driving engine.